1) Field of the Invention
The invention relates to graft copolymers having improved phase binding between the graft base and the grafted-on polymer phase, to the peroxy group-containing copolymers on which these are based, and to copolymerizable peroxy monovinyl esters. The invention furthermore relates to processes for the preparation of said polymers and peroxy compounds.
2) Background Art
Copolymerizable initiators offer interesting opportunities in the preparation of novel polymeric materials. By means of such initiators, potential free-radical functions which function as defined anchor groups in the preparation of graft and block copolymers, are introduced into polymer chains. One area of application is, for example, the phase coupling of incompatible polymers in core/shell latices during the preparation thereof by the emulsion polymerization process.
Peroxy carbonates containing an allylic double bond and the use thereof as comonomers in copolymerization with further ethylenically unsaturated monomers are described in DE-A 2726008. German Patent 3420048 relates to copolymers of vinyl acetate and peroxyallyl carbonates and the use thereof as sizing agents for glass fibers. It is disadvantageous that these allyl-functional peroxy carbonates only copolymerize very slowly, if at all, with other vinyl monomers.
EP-A 277608 (U.S. Pat. No. 4,879,347) and EP-A 279430 (U.S. Pat. No. 4,839,432) describe copolymerizable peroxy carbonates containing (meth) acrylate and allyl ether functions as comonomers for improving the phase binding in the preparation of polymer blends. The peroxy carbonate is polymerized here with vinyl monomers in the presence of an ethylene copolymer by the suspension polymerization process. On heating of the mixture, coupling of the two polymer phases takes place via the peroxy functions. U.S. Pat. No. 4,923,956 describes a procedure which is analogous to EP-A 279430, with the difference that propylene polymers are employed instead of the ethylene polymers. EP-A 307802 relates to mixtures of polypropylene, a further polymer and copolymer made from a vinyl monomer and a peroxy carbonate containing an allyl ether or (meth) acrylate function; the phase binding thereof being improved by heating to temperatures of from 200.degree. to 300.degree. C. EP-B 225091 describes allyl ether-substituted peroxy dicarbonates used as initiators for the preparation of high-molecular-weight, branched VC polymers. The above-mentioned copolymerizable peroxy esters, in particular the allyl compounds, have the disadvantage of low reactivity on copolymerization with other vinyl monomers. Further more, said peroxy esters can only initiate further free-radical reactions from temperature.gtoreq.130.degree. C. and are thus of no interest for emulsion polymerization.
The known methylstyrene-based peroxy compound discussed by W. C. Endstra in Kautschuk und Gummi, Kunststoffe 42(5), 414 (1989) has the disadvantage that it cannot be copolymerized with many vinyl monomers, and further free-radical reactions are only initiated thermally from temperatures.gtoreq.160.degree. C. The same applies to tert.-butyl-peroxy (p-(vinylbenzoyl) benzoates (I. Gupta, S. N. Gupta, D. C. neckers, J. Polym. Sci.: Polym. Chem Ed. 20, 147 (1982), which only thermally initiate further free-radical reactions from T.gtoreq.100.degree. C. and thus cannot be employed for copolymerization by the emulsion polymerization process.
The object was therefore to provide olefinically unsaturated peroxy compounds which are copolymerizable with ethylenically unsaturated monomers whose peroxy group is retained during the copolymerization and whose peroxy groups, after incorporation into the copolymer, are able to initiate further free-radical polymerization reactions at temperatures.ltoreq.100.degree.. A further object was to provide these peroxy compound-containing copolymers and the graft copolymers based on the peroxy group-containing copolymers.
Surprisingly, we have found that this object is achieved by means of peroxy monovinyl esters of aliphatic dicarboxylic acids and copolymers or graft copolymers containing these peroxy compounds.